1. Field of the Invention
The present invention relates to fluid-flow control devices in general, and more particularly to electromagnetically controlled seat valves.
2. Description of the Related Art
There are already known various constructions of electromagnetically controlled pressure regulating valves, among them that disclosed in the German patent publication DE 44 31 457 C2. In order for the characteristic response lines of this known pressure regulating valve to exhibit behavior that is to a large extent independent of the temperature and thus of the viscosity of the pressurized medium, the valve connection element of this pressure regulating valve is provided with a throttling orifice in the pressurized medium supply path which includes sections of differing cross-sectional shapes. A throttling device of this kind presents a resistance to the flow of the pressurized medium, which reduces the pressure that is in effect at the valve seat. As a result, the range over which the pressure of the medium can be regulated is increased, with simultaneous reduction in the temperature-dependent resistance contribution of the valve seat. Therefore, the pressure regulating valve of this construction exhibits a reduced residual pressure, that is reduced differences between the characteristic response lines applicable when the pressurized medium is warm and cold, respectively.
In order to achieve a minimum residual pressure, the throttling device must effect a considerable pressure build-down or reduction at very cold temperatures of the pressurized medium. This, however, is accompanied by a low volume of flow through this conventionally constructed pressure regulating valve. Yet, at relatively high temperatures, that is when the pressurized fluid exhibits relatively low viscosity, the unavoidably leakage in the user circuit that is connected to the pressure regulating valve is so high that a high flow-through volume of the pressurized medium through the valve would be required to compensate for it, lest the regulated pressure of the pressurized medium suffer detrimental consequences, such as a pressure breakdown. In order to fulfil these countervailing requirements in the most optimal manner achievable, the pressure regulating valve should have as high a ratio between the flow-through volume at high and low temperatures of the pressurized medium as possible or feasible. Unfortunately, the values of this obtainable by using the pressure regulating valve of this known constructions leave much to be desired at least as far as certain applications of the valve are concerned.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide an electromagnetically controlled seat valve that does not possess the drawbacks of the known valves of this type.
Still another object of the present invention is to devise a valve of the type here under consideration in which the ratio between the flow-through volumes at high and low temperatures would exceed that available from known valves of this type.
It is yet another object of the present invention to design the above valve in such a manner that differences between its characteristic response lines at high and low temperatures are improved relative to those of the prior art.
A concomitant object of the present invention is so to construct the valve of the above type as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides in an electromagnetically controlled seat valve that includes a hollow housing bounding a user channel having one end to be connected to a hydraulic medium user and another end, and respective supply and a discharge channels communicating with the interior of the housing between the ends, and at other end of the user channel, respectively. A closing member is mounted in the housing for movement toward and away from a closing position in which it sealingly separates the user channel from the discharge channel. Further accommodated in the housing, at the other end of the user channel, is means for applying a variable closing force to the closing member to urge the latter toward the closing position thereof, such applying means including an electrically energizable coil, an armature mounted between the coil and the closing member for relative movement in response to electromagnetic forces exerted by the latter when energized, and a return spring urging the armature in a direction corresponding to the closed position of the closing member. Last but not least, there is provided throttling means interposed between the supply and user channels for determining the amount of the hydraulic medium supplied into the user channel and hence the force with which this medium acts on the closing member against the variable closing force to open the closing member and thus establish a pressure-relieving communication between the user and discharge channels, such throttling means including in accordance with the present invention at least two throttling orifices extending in fluid flow parallelism with one another between the supply and user channels and each having a length and a transverse dimension that are in a ratio of at least 2:1.
A particular advantage obtained by using the seat valve of the present invention as described so far is that the ratio between the flow-through pressurized medium volume at high and low temperatures is significantly improved as compared with the state of the art, as a result of the special construction of the throttling device or means as proposed by the present invention. To this end, the single orifice of a larger size that had been customarily used up to now has been replaced in accordance with the present invention with a plurality of smaller-size throttling orifices that are spaced from each other but are arranged parallel to one another as far as the flow of the pressurized medium through them is concerned. Individual throttling orifices with smaller sizes have a higher throttling effect on the medium flowing through them, and hence permit less of the medium to flow through them, at relatively low temperatures than the aforementioned larger-size single throttling orifice. On the other hand, the flow-through volume needed for reliable operation at higher temperatures can be assured by appropriately choosing the number of the individual throttling orifices.
According to a articularly advantageous feature of the present invention, the housing includes a wall portion that bounds the user channel at the supply channel, separating these channels from each other, and the throttling orifices extend through this wall portion substantially radially with respect to the user channel, being distributed over the circumference of the wall portion. The throttling orifices may advantageously have flow-through cross-sectional areas of sizes and/or shapes that are different from one another. As a result of this, the pressure regulating valve can be fitted to various requirements that may be applicable for different instances of use of a valve of this construction.
It is especially advantageous when, in accordance with another facet of the present invention, the housing includes an injection-molded valve part of a synthetic plastic material that is provided with the supply, user and discharge channels in a ready-to use form during the injection molding process of its manufacture. When this approach is being used, hardly any extra expenses are incurred as the result of the provision of the plurality of throttling orifices. It is also advantageous when the pressure regulating valve is constructed as a seat valve in that its housing includes a valve seat surrounding the other end of the user channel and the closing member cooperates with the valve seat to interrupt and establish communication past the latter between the user and discharge channels.
The present invention is also directed to an automatic transmission for a motor vehicle, which includes an electromagnetically controlled seat valve of the above construction, that is one including a hollow housing bounding a user channel having one end to be connected to a hydraulic medium user and another end, and respective supply and a discharge channels communicating with the interior of the housing between the ends, and at other end of the user channel, respectively; a closing member mounted in the housing for movement toward and away from a closing position in which it sealingly separates the user channel from the discharge channel; means in the housing at the other end of the user channel for applying a variable closing force to the closing member to urge the latter toward the closing position thereof, including an electrically energizable coil, an armature mounted between the coil and the closing member for relative movement in response to electromagnetic forces exerted by the latter when energized, and a return spring urging the armature in a direction corresponding to the closed position of the closing member; and throttling means interposed between the supply and user channels for determining amount of the hydraulic medium supplied into the user channel and hence the force with which this medium acts on the closing member against the variable closing force to open the closing member and thus establish a pressure-relieving communication between the user and discharge channels, including at least two throttling orifices extending in fluid flow parallelism with one another between the supply and user channels and each having a length and a transverse dimension that are in a ratio of at least 2:1. Automatic transmissions of this construction, i.e. including the valves constructed in accordance with the present invention, show improved performance over those of the prior art, especially as far as their gear-switching properties under various operating conditions are concerned.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.